Figure 1.

Stochastic model of cell turnover. Left panels: given is the schematic description of the finger-like (A), hemispheric (B), and circular disk (C) structures of the epithelium. Cells enter the epithelium from the crypts (blue arrows) and shed from the tips or the center of the structures (red arrows). L_f, L_h, and L_c, as indicated by double lines, are the lengths of the shortest path between the crypt orifices and the shedding sites. Right panels: shown are the stochastic processes of cell turnover in respective structures. τ_f, τ_h, and τ_c are the cell migration times for the shortest paths of the respective structures. Each structure has a total of N cells in the epithelium and chooses n red-colored cells as the shedding cells from those aged above the shortest-path cell migration times, i.e., the cells surrounded by the dashed-line frames. After the remaining intraepithelial cells have incremented their ages by 1, n blue-colored cells of age 1 are supplied into the epithelium from the crypts. To see this figure in color, go online.